Temperature control instruments



INVENTOR,

C. H. STRANGE TEMPERATURE CONTROL INSTRUMENTS Filed Jan. 28, 1954 April 5, 1955 /4 TTONEY Patented Apr. 5, 1955 2,705,747 TEMPERATURE CONTROL INSTRUMENTS Charles H. Strange, Jacksonville Beach, Fla., assignor to Elsa L. Strange, Jacksonville Beach, Fla.

This invention relates to temperature responsive or control instruments for use up to about 2400 F. and more particularly to improvements in such devices as described in my co-pending application Serial Number 330,195, tiled January 8, 1953, and Serial Number 389,278, tiled October 30, 1953.

In the latter application I disclosed a thermocouple of two alloys or metals Inconel and Kanthall and the compositions of each metal.

It is an object of this invention to provide an instrument of the type described in said application, Serial Number 389,278 in which one thermostat expansion element also functions as an element of a thermocouple. Such a combination affords many outstanding advantages not only because the above mentioned therthermal E. M. F. almost exactly equal to that of the much more expensive platinum-rhodium couple, but because the readings of the E. M. F. indicate the conditions of the thermostat elements.

The inventive features for attaining these and many more objects are shown herein in connection with a temperature responsive instrument which briey described includes an element serving as a thermocouple element and an expansion element at the same time and formed from a cheap known metal.

In the accompanying drawing showing, by way of example, one of many possible embodiments of the invention:

The drawing shows a longitudinal cross section of the instrument.

Inconel is a known alloy melting at about temperatures of the order of 2500 F. and composed ot' approximately 79.5% Ni; 13% Cr; 6.5% Fe; 0.25% Mn; 0.25% Si; 0.20% Cu; and 0.08% C and having a coeicient of expansion of about 0.64 *5.

Kanthall is likewise a known alloy melting at temperatures of the order of 2750 F. and is composed of approximately 0.25 max. C; 0.3-2.0% Si; 18-25% Cr; 3 5-6.5% Al; nil-3.0% Co; nil-3.0% Ta; 0.2-1.0% Mn and the balance Fe, and having a coecient of expansion of the same order as that of InconeL Hereinafter Inconel is sometimes referred to as alloy A and Kanthall as alloy B.

The device comprises a tube or expansion element 10 of Inconel closed at the inner end 11 except for a small hole 12 therein and adapted to be disposed through a hole 14 in a kiln wall 15. Within the end portion 16 of the tube 10, which project into the kiln, there is disposed a porcelain tube 18 which does not soften below about 3000o F. While porcelain is the preferred material, other materials having high melting or softening points of the order of 3000 F. and above, negligible thermal expansion, and high electrical insulating properties may be used.

The inner end 19 of the porcelain tube abuts against the end 11 of the outer metal tube 10 while the outer end 20 of porcelain tube is free to move relative to the outer tube 10 due to expansion and contraction of the tube portion 16 during temperature changes. The porcelain tube undergoes virtually no expansion and contraction over a wide range of temperature, and there is relative movement between the end 20 and the adjacent portion of the tube 10 due to the great dilerence in expansion of porcelain and metal. Y

Relative movement of the tube end 20 and the tube 10 thereat, is transmitted beyond the outer end 21 of the tube 10 by a transmission rod or member 22 of Kanthall having an end 24 easily tting Within the bore 25 of the porcelain tube and shoulder 26 against the end 20 and out of contact with the metal tube 10.

22 extends coaxially with the tube 10 beyond the end 21 thereof and is disposed 28 of hard electrical insulating material such as asbestos board secured on the end 21 of tube as by a screw 29. The opening 30 of the bearing may be bushed as at 31 with metal to aiord easy movement if desired, but the rod must not come in electrical contact with the end of' the tube 10. A spring 32 compressed between a shoulder 34 on the rod inner of the bearing and the bearing urges the rod and porcelain tube inwardly so that there is never any lost motion between the two.

The portion 35 of the rod passing out through the bearing is employed to actuate a control button 36 of cured fast to the tube 10 rod end 3S with a cap 48 with a strong spring 49 therein, so that when the portion 16 of the tube 10 room temperature.

The coecients of expansion to Inconel and Kanthall are of the same order and very nearly the same. o material error arises due to expansions of the rod Thus far the description has concerned merely a thermostatically controlled or actuated switch and such a device would be operative. The adaptation of such a device to form a thermometer as well as the thermostat requires no change and very few additions.

As stated in my above mentioned application Serial Number 389,278 the Inconel-Kanthall thermocouple has almost the identical characteristics as has the platinum-rhodium couple, up to about 2400 F. The characteristics are about the same both as to the E. M. F. and the E. M. F.temperature coeicient..

In adapting the above described instrument I have disposed a Kanthall wire 50 in the bore of the porcelain tube 18 and welded one end weld at S2 constituting the A piece 54 of Kanthall is welded onto the end 21 the tube 10 in the housing 40 and this constitutes cold junction. Suitable conductor leads S5 and 56 are attached as at 58 and 59 to the piece 54 and to a Kanthall part of the rod 22. E. M. F. or temperature values may be indicated by a suitable meter 60 connected to the leads 55 and 56 and which may be mounted on the housing.

In use the meter 60 and dial 46 are calibrated for de- .sired scales.

piece must be of metal A. An interchange of metals of course requires that the leads 54 and 55 be swapped A having the approximate composition Per cent Ni 79.5 Ci' 13.0 Fe 6.5 Mn 0.25 Si 0.25 Cu 0.20 C 0.08 and B having the composition Per cent C 0.25 max Si 0.3-2.0 Cr 18-25 A1 3.5-6 5 Co Nil-3 0 Ta Nil-3 0 Mn 0.2-1.0 Fe Balance 2. In a temperature responsive instrument, a metallic tube substantially closed at the inner end and having a porcelain tube therein coaxially therewith and abutting against said tube end, member of different metal from that of the tube and insulated therefrom and in the metallic tube and havan end of the porcelain tube, the from the outer end of the metal tube, the member being for transmitting relative movement o longitudinal expansion of the tubes, a switch substantially fixed with respect to the outer end of the metal tube and having a part adapted to be engaged by the outer end of the member, the metals of the member and tube having a melting point as high as about 2400" F., coefficients of thermal expansion of the same order and greater than that of porcelain, and having different temperature-E. M. F. relationships.

3. In a temperature responsive instrument, a metallic tube substantially closed at the inner end and having a porcelain tube therein coaxially therewith and abutting against said tube end, a rod-like transmission member of different metal from that of the tube and insulated therefrom and in the metallic tube and having a part against an end of the porcelain tube, the member projecting from tube, the member being for transmitting relative movement of longitudinal expansion of the tubes, a switch substantially fixed with respect to the outer end of the metal tube and having a part adapted to be engaged by the outer end of the member, the metals of the member and tube having a melting point as high as about 2400 F., coeflicients of thermal expansion of the same order and greater than that of porcelain, and having different temperature-E. M. F. relationships, and a conductor of the same metal as that of the transmission in the bore of the porcelain tube and having one end electrically secured to the member and the other end to the inner end of the metal tube.

4. In a temperature responsive instrument, a metallic tube substantially closed at the inner end and having a porcelain tube therein coaxially therewith and abutting against said tube end, a rod-like transmission member of different metal from that of the tube and insulated therefrom and in the metallic tube and having a part against an end of the porcelain tube, the member projecting from the outer end of the metal tube, the member being for transmitting relative movement of longitudinal expansion of the tubes, a switch substantially xed with respect to the outer end of the metal tube and having a part adapted to be engaged by the outer end of the member, the metals of the member and tube having a melting point as high as about 2400 F., coefficient of thermal expansion of the same order and greater than that of porcelain, and having a rod-like transmission different temperature-E. M. F. relationships, one metal A having approximately the composition Per cent Ni 79.5 Cr 13.0 Fe 6.5 M n 0.25 Si 0.25 Cu 0.20 C 0.08 and the other metal B having the composition Per cent C 0.25 max. Si 0.3-2.0 Cr 18-25 Al 3.5-6.5 Co Nil-3.0 Ta Nil-3.0 Mn 0.2-1.0 Fe Balance 5. An instrument as claimed in claim 3, one metal A having the approximate composition Per cent N1 79.5 Cr 13.0 Fe 6.5 Mn 0.25 Si 0.25 Cu 0.20 C 0.08 and the other metal B having the composition Per cent C 0.25 max Si 0.3-2.0 Cr 18-25 Al 3.5-6 5 Co Nil-3 0 Ta Nil-3.0 Mn 0.2-1.0 Fe Balance 6. An instrument as claimed in claim 5, the metal tube being of metal A.

7. In an instrument as claimed in claim 3 and a piece of metal of the same as that of the wire welded onto connected to 8. In an instrument as claimed A having approximately the composition:

Co Nil-3 0 Ta Nil-3 0 Mn 0.2-1 0 Fe Balance 9. In an instrument as claimed in claim 3, the metal tube having the double function of an expansion and thermocouple element.

References Cited in the tile of this patent UNITED STATES PATENTS Burling Aug. 6, 1940 Titcomb Ian. 29, 1946 

4. IN A TEMPERATURE RESPONSIVE INSTRUMENT, A METALLIC TUBE SUBSTANTIALLY CLOSED AT THE INNER END AND HAVING A PORCELAIN TUBE THEREIN COAXIALLY THEREWITH AND ABUTTING AGAINST SAID TUBE END, A ROD-LIKE TRANSMISSION MEMBER OF DIFFERENT METAL FROM THAT OF THE TUBE AND INSULATED THEREFROM AND IN THE METALLIC TUBE AND HAVING A PART AGAINST AN END OF THE PORCELAIN TUBE, THE MEMBER PROJECTING FROM THE OUTER END OF THE METAL TUBE, THE MEMBER BEING FOR TRANSMITTING RELATIVE MOVEMENT OF LONGITUDINAL EXPANSION OF THE TUBES, A SWITCH SUBSTANTIALLY FIXED WITH RESPECT TO THE OUTER END OF THE METAL TUBE AND HAVING A PART ADAPTED TO BE ENGAGED BY THE OUTER END OF THE MEMBER, THE METALS OF THE MEMBER AND TUBE HAVING A MELTING POINT AS HIGH AS ABOUT 2400*F., COEFFICIENT OF THERMAL EXPANSION OF THE SAME, 